Effects of exhaustive exercise on blood‐O 2 transport in northern leopard frogs ( Rana pipiens )

Abstract

Previous studies suggest that anaerobic activity in anurans enhances aerobic metabolism during nonsustainable locomotion (see Gatten et al. 1992). To test the hypothesis that lactic acidosis promotes blood-O2 transport, adult R. pipiens were subjected to daily bouts of exhaustive hopping exercise for 3 wk. Anaerobic locomotion caused a significant metabolic and respiratory acidosis. In vivo blood acid-base properties for exercised frogs at 22oC were pH 7.27, PCO2 = 23 Torr, and [Lact] = 14 mM; corresponding values for resting animals were pH 7.85, PCO2 = 9 Torr, and [Lact] = 1 mM. O2 equilibrium curves (O2EC) were generated at 22oC by thin-film techniques. Anaerobic exercise caused a significant reduction in blood-O2 affinity; P50's for exercised and resting frogs were 43 and 37 Torr, respectively. Exogenous lactic acid, added to whole blood from resting animals and to purified frog hemoglobin solutions, caused similar reductions in Hb-O2 affinity. The maximum effect of exogenous lactic acid on whole blood P50 was achieved at [Lact] = 8–14 mM. These effects of exhaustive anaerobic exercise and exogenous lactic acid on Hb-O2 affinity were solely pH (Bohr effect) phenomena. The O2 binding curves generated for both whole blood and purified Hb solutions exhibited complex O2EC shapes; Hill coefficients (n) increased with increasing Hb-O2 saturation. Exhaustive exercise also caused rapid (~5 min) and significant reductions in Hct (25%) and [Hb] (30%), with no change in RBC volume. We conclude that lactic acidosis resulting from nonsustainable hopping activity in frogs promotes tissue O2 delivery without compromising pulmonary O2 loading. (Supported by DePaul Univ. LA&S grant)